This Lizard Displays an Unusual Aquatic Adaptation (Video)

One of the reasons I love reptiles and amphibians is that they display some absolutely incredible adaptations to survive. Some adaptations, while effective, aren't too surprising to those who observe them, but every now and then, biologist stumble across something a little bit more interesting. This was the case for a Costa-Rican lizard species known as the water anole (Anolis aquaticus).

At first glance, the water anole doesn't appear all that unique from other anole species, but it is its behavior that sets it apart. When confronted with danger, most anoles take off, darting rapidly into the tree tops or small holes for cover. As its name suggests, the water anole takes a different approach: it dives into the water and waits for the predator to leave, sometimes remaining submerged for as long as 16 minutes. There may be animals that can remain submerged for far longer than 16 minutes, but the water anole does something that has not been observed in any other reptile species.

Lindsey Swierk (assistant research professor of biological sciences at Binghamton University, State University of New York) documented that the anole is actually still breathing underwater with a sort of biological "scuba tank" system consisting of a recycled air bubble that clings to its head. 

 "Diving under water and remaining there for a long time is an anti-predator strategy for water anoles. These lizards aren't particularly speedy, and taking to the water is a very effective option. (Take it from a biologist who sometimes struggles to capture her study organism because they're so good at diving.) It's easy to 'disappear' to a predator's eye once you hide under water for a few minutes. I think that any underwater breathing adaptations in water anoles would have arisen to extend the amount of time they can stay in their underwater refuge." -Swierk Source

Swierk observed an anole exhaling and re-inhaling this air pocket underwater. She believes that there is a gas exchange going on between this large bubble and other smaller bubbles around the lizard's head. She also noted the way the bubble clings to the anole's face; it seems there is likely physiological adaptation that holds the bubble in place.

 "I think it's possible that some additional air pockets are being trapped around the anole's head and throat, and that the inhalation and exhalation of the air bubble allow for some trading of fresh air among these air pockets, allowing the anole to swap air in its current air bubble with 'new' air. It's additionally possible that the air bubble plays a role in allowing an anole to get rid of carbon dioxide. I suspect that there might be morphological adaptations, namely the shape of the top of the anole's head, which allows a large bubble of air to cling to it easily." -Swierk Source

Swierk plans to continue her research into the bizarre breathing habits of the anole. An analysis of their stomach contents also revealed insects that largely live underwater, meaning that these anoles are likely diving for more reasons than to just escape predators. 

 "If future investigation reveals that this rebreathing behavior is adaptive, then I would imagine that it is a trait that evolved over time to allow water anoles, and perhaps similar anole species, to thrive in their aquatic habitats." -Swierk Source

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Article Link: https://phys.org/news/2019-03-scuba-diving-lizard-underwater-minutes.html